It is known in the art of high speed optical communication systems that more than one wavelength may be used to carry information. In particular, each optical wavelength may be a carrier for digital or analog communication signals. Also, an optical switch may be used to discriminate on a wavelength basis as to which wavelengths get routed to which output(s) of the switch.
One prior art technique to couple a plurality, of wavelengths, e.g., 8, onto a signal fiber employs an arrangement of 2.times.2 couplers as shown in FIG. 1. In particular, two different wavelengths are fed into each 2.times.2 coupler in an input stage. A single output from each of the 2.times.2 couplers is fed to a second stage, where a single output from each pair of couplers is combined by another 2.times.2 coupler. A single output from each of the 2.times.2 couplers in the second stage is then fed to a third stage where each pair of outputs from the second stage is combined by another 2.times.2 coupler in the third stage.
The prior art arrangement shown in FIG. 1 couples eight wavelengths on eight separate fibers at the input stage to a single fiber at the output of the output stage. However, because there are three stages of coupling which occurs, and each stage incurs a 3 dB loss in the signal coupled, the total loss for a eight wavelength to one fiber coupling would be 87.5% loss (or 9 dB).
Thus, it would be desirable to obtain a device for efficient low loss multiplexing of a plurality of wavelengths onto a single optical fiber.